The present invention relates to systems and methods for reducing wind loads on monopoles, such as telecommunication structures or antenna towers, for example.
Tall antenna towers are typically constructed as multi-sided polygonal structures, typically having on the order of eight to eighteen sides. When exposed to high winds, such antenna towers experience high wind loads, and often times require reinforcement to keep them from becoming overstressed per government structural codes.
A common conventional approach to structural reinforcement of an antenna tower welds multiple reinforcing members along the length of the tower. This conventional approach is very expensive, costing on the order of $1000 per foot for a typical antenna tower.
It has been common to retrofit polygonal steel monopole towers to add additional antenna carriers. The retrofit schemes that are currently used in the tower industry are common in one major respect: they are reinforcement methods. In order to accommodate the additional carriers, the structural capacity of the tower is increased, either by augmenting individual components or by adding external structures to support the existing tower while sustaining higher loads.
Wind loading governs the design of all steel antenna-supporting structures as per the TIA/EIA-222-F, which is the commonly accepted standard. The tower profile determines the drag force coefficient, which is linearly proportional to the wind load.
A number of US patents and patent applications relate to telecommunication structures, such as antenna towers and poles, which are discussed below.
U.S. Pat. No. 1,732,690 discloses “devices designed to rotatably support loop antennas.” (see Abstract)
U.S. Pat. No. 3,958,381 discloses a “Concrete filled tapered tubular tower” (Title).
U.S. Pat. No. 5,060,435 discloses a “Bracket for support of a vertical pole” (Title).
U.S. Pat. No. 6,028,566 discloses “an aerial tower 15, also referred to as a monopole or simply a pole is shown which at a lower end is typically mounted upon a footing that is located adjacent to a shelter that contains radio frequency for RF equipment associated with wireless communication networks. The aerial tower 15 may be of any conventional design at least including hollow tubular steel columns 17 through which communication wiring is housed between a top end and lower end of the tower 15 and self supporting and guyed towers.” (see Abstract)
U.S. Pat. No. 6,131,349 discloses with reference to FIGS. 10 and 11, “an enclosure and antenna tower support unit in accordance with the invention is illustrated and generally designated by the numeral 320. The enclosure unit 320 includes an enclosure 224 supported on a support base 222 on which a generally rectangular reinforcing deck plate 322 is suitably secured, such as by welding. Support base 222 is modified slightly to include longitudinal intermediate beams 70c, see FIG. 11 also, which are of generally rectangular tubular cross sectional configuration. Spaced apart bolt stiffening and support plates 324 extend between the beams 70c and are suitably welded thereto and to form supports for elongated studs or bolts 326, FIG. 11, which are operable to be connected, as shown, to a generally cylindrical base member 328 of a tubular, polyhedral cross section, tapered monopole type tower 330 of a type known in the art for supporting floodlights, electrical transmission lines and other items requiring elevation above ground level. Suitable communications antenna 43a may, of course, be mounted on the tower 330 in the same manner as the antenna 43a are mounted on the tower 228, for example. Use of the tubular monopole type tower 330 may be preferred in certain applications of telephone and other wireless communications equipment in the interest of reduced costs and weight.” (see column 8, line 61 to column 9, line 17)
U.S. Pat. No. 6,222,503 discloses “System and method of integrating and concealing antennas, antenna subsystems and communications subsystems” (Title).
U.S. Pat. No. 6,256,961 discloses a “Utility pole base construction” (Title).
U.S. Pat. No. 6,322,863 discloses a “Utility pole with pipe column and reinforcing rods comprised of scrap rubber and plastic” (Title).
U.S. Pat. No. 6,446,408 discloses a “Collapsible pole”, and more particularly an “apparatus and method for elevating items includes telescopically retractable and extendable hollow tubular pole sections that include a locking means to lock at least one section in extended position. The bottom of the pole is adapted for mounting to a support structure.” (see Abstract)
U.S. Pat. No. 6,453,636 discloses a “support structure for use with an existing single pole tower. The single pole tower has a pole anchored to a foundation and supports a first load. The support structure has a number of sleeves surrounding the pole. A first one of the sleeves is anchored to the foundation. A second load is attached to a second one of the sleeves.” (see Abstract)
U.S. Pat. No. 6,694,698 discloses “Reinforcement apparatus for monopole towers” and more particularly, “a reinforcement apparatus forming an exo-skeleton of tubular steel rods and adjustable mounting clamps directly in contact with the exterior of previously erected tapered wireless communication monopole towers to provide additional strength and resistance against deflection due to wind forces and additional weight thereby enabling the placement of more antenna arrays and communication instruments thereon.” (see Abstract)
US Patent Application No. 2002/0140623 discloses that an “existing monopole is strengthened to accommodate loading associated with additional elements included in over-the-air communications systems by placing expanding foam and aggregate, light weight aggregate concrete, normal weight aggregate concrete or other types of fill material into the hollow bore in the interior of the monopole. Monopole strengthening may require base plate strengthening, adding anchor bolts and/or foundation strengthening. This permits an existing monopole to accommodate more elements than were initially envisioned when the monopole was initially erected.” (see Abstract)
US Patent Application No. 2003/0000165 discloses an “precast post-tensioned segmental pole system capable of supporting a load is provided. The pole system includes a plurality of pole segments that use connectors and strands to anchor them together. The strands extend within a cavity formed in the pole segments and are external to the wall structure of the pole segments. The strands may be coupled between both of the pole segments, or be anchored to a connector. The connector includes an upper piece that is coupled to one pole segment, and a lower piece that is coupled to the other pole segment. Upper and lower pieces interlock with each other to join the pole segments to one another. The strands are placed in tension so that pole system is capable of withstanding forces imposed by the load.” (see Abstract)
US Patent Application No. 2003/0026923 discloses an “integrated, monopole reinforcement sleeve system for the reinforcement of self-supporting monopoles at select, predetermined locations. The integrated, monopole reinforcement sleeve system is composed of at least one pair of complementary hemi-sleeves and a non-slip filler, wherein the filler is inserted between the sleeves and the monopole. The sleeves are tightened around the monopole, thereby providing integrated monopole reinforcement. A method for the reinforcement of monopoles with an integrated reinforcement sleeve is also described.” (see Abstract)
US Patent Application No. 2003/0033281 discloses a “support structure for use with an existing single pole tower. The single pole tower has a pole anchored to a foundation and supports a first load. The support structure has a number of sleeves surrounding the pole. A first one of the sleeves is anchored to the foundation. A second load is attached to a second one of the sleeves.” (see Abstract)
US Patent Application No. 2004/0020158 discloses a “tower reinforcement apparatus designed to increase the load capacity and stability of a tower to enable the tower to support the weight of additional communication equipment as well as the environmental forces exerted on the tower. The preferred embodiment generally includes upper and lower collar assemblies disposed about the tower, a plurality of mounting blocks having a flat portion that is secured to an outer surface of the tower and an inner surface of the upper or the lower collar assemblies to secure the collar assemblies to the tower, a plurality of flat bars vertically attached to the upper and the lower collar assemblies, and at least one ring disposed between the collar assemblies, the at least one ring is formed to wrap around the tower and the flat bars in order to hold the flat bars in compression with the tower.” (see Abstract)
US Patent Application No. 2004/0070985 discloses a “modular pole system and light fixture is disclosed wherein the modular pole system is comprised of an internal skeletal structure and an external plastic shell. The external plastic shell may slide over the assembled internal skeletal structure and may be comprised of a singular unit. The internal skeletal structure may be comprised of an upwardly extending tapered pole which is held in place by a base and post which also provides a static structure acting as a passive defense mechanism.” (see Abstract)
However, none of the above-cited patents or applications disclose or suggest attaching a series of segmented conical sections to a polygonal tower or pole to reduce wind loads. It would be desirable to have a technique for reducing wind loads on antenna towers and monopoles exposed to winds that does not require structural reinforcement of the tower or pole, improves upon conventional techniques and lowers costs of implementation.